1. Field of the Invention
The present invention relates to a rectangular unit box for a fuel cell containing a stack body as a cell stack formed by stacking a large number of unit cells. Further, the present invention relates to the fuel cell.
2. Description of the Related Art
In general, a fuel cell is formed by placing a stack body as a cell stack formed by stacking a large number of unit cells in a rectangular unit box. In the structure, after the cell stack is used for a certain period, maintenance operation is required for the cell stack. For example, if any of the unit cells has a defect without reaching the desired output level, the defective unit cell needs to be replaced with a new unit cell. For this purpose, in the unit box, hinges are used for detachably coupling panels together into a box shape so that the unit box can be assembled, and disassembled easily (see Japanese Laid-Open Patent Publication No. 2002-298901).
Conventionally, as the hinges used for the unit box of this type, for example, hinges 2 as press parts as shown in FIGS. 8 and 9 are used. Each of the hinges 2 has a tab 2a and a joint plate portion 2b. The tab 2a is folded into a tube shape to have a pin through hole 1 for engagement with a joint pin under pressure. The joint plate portion 2b is joined to an edge of the panel 3 by spot welding or using a bolt.
However, in the unit box of the fuel cell, during operation of the fuel cell, the internal pressure generated when thermal expansion of the cell stack occurs, or the high internal pressure of the fuel gas such as a hydrogen-gas flowing through the flow field is applied to the hinges. Therefore, the panels need to be securely coupled together with high mechanical strength. Further, the components need to be fabricated with high degree of accuracy to achieve the desired air-tightness for preventing leakage of gases to the outside. Though the conventional hinges can be produced at low cost as press parts, since the tabs 2a are simply fabricated by folding under pressure, the accuracy in fabrication of the tabs 2a is low. For example, the pin through hole 1 in the tab 2a may not have the perfectly circular shape. As a result, the pin through hole 1 is not engaged with the joint pin precisely. Therefore, the air-tightness is low. Further, the panels are not securely coupled together.
In an attempt to address the problem, in a conventional approach, as the hinges of the unit box, hinges 4 as shown in FIGS. 10 and 11 are adopted. The hinges 4 are formed integrally with an edge of a panel 3 by machining (cutting).
However, since the hinges 4 are formed by cutting, fabrication of the hinges 4 is laborious, and time consuming. Further, since the number of steps in fabrication is large, the hinges 4 are produced at significantly high cost.